Experimental study on the role of 5-HT2 serotonin receptors in the mechanism of anti-inflammatory and antihyperalgesic action of antidepressant fluoxetine.

INTRODUCTION Fluoxetine is an antidepressant that has anti-inflammatory and antihyperalgesic effects in experimental models of pain and inflammation. The AIM of the present study was to determine the role of 5-HT2 receptors in the mechanism of anti-inflammatory and antihyperalgesic action of fluoxetine after single and repeated administration of the drug. MATERIALS AND METHODS 40 male Wistar rats were randomly divided in five groups (n = 8) treated for 14 days with saline (control), diclofenac (positive control), fluoxetine, cyproheptadine (5-HT2 antagonist), and fluoxetine + cyproheptadine, respectively. We used the experimental model of inflammation induced by intraplantar injection of carrageenan and nociceptive test with mechanical pressure on the inflamed hind paw. RESULTS Single and repeated administration of fluoxetine showed that it had significant anti-inflammatory and antihyperalgesic effects when compared with the control (p < 0.05). Cyproheptadine did not change significantly the anti-inflammatory effect of fluoxetine in the first 4 hours, after a single administration. At 24 hours the combination did not differ statistically when compared with the control. Cyproheptadin did not change significantly the anti-inflammatory effect of fluoxetine after repeated administration. After prolonged treatment the group that received fluoxetine + cyproheptadine showed a statistically significant increase in paw pressure to withdraw the hind paw compared with that treated with fluoxetine alone (p < 0.05). CONCLUSIONS Fluoxetine has anti-inflammatory and antihyperalgesic effects in the carrageenan model of inflammation. 5-HT2 receptor mediated its anti-inflammatory effect in single dose treated animals. Spinal 5-HT2 receptors are involved in the antihyperalgesic effect of fluoxetine after repeated administration.